“Houston We Have a Podcast” is the official podcast of the NASA Johnson Space Center, the home of human spaceflight, stationed in Houston, Texas. We bring space right to you! On this podcast, you’ll learn from some of the brightest minds of America’s space agency as they discuss topics in engineering, science, technology and more. You’ll hear firsthand from astronauts what it’s like to launch atop a rocket, live in space and re-enter the Earth’s atmosphere. And you’ll listen in to the more human side of space as our guests tell stories of behind-the-scenes moments never heard before.
Dr. Steve Johnson, Senior Scientist of the Space Radiation Analysis Group, discusses what’s being done right now to document radiation exposure, not only to ensure our astronauts stay healthy, but to understand weather in space. This podcast episode was recorded on August 14, 2018.
Check out the “Space Radiation Analysis Group” website.
Transcript
Gary Jordan (Host): Houston, we have a podcast. Welcome to the official podcast of the NASA Johnson Space Center, episode 64, Space Weather. I’m Gary Jordan and I’ll be host today. So, in this podcast, we bring in the experts, NASA scientists, engineers, and astronauts, all to let you know what’s going on right here at NASA. So, if you’re familiar with us, you’ll know that we recently just completed a five-part series on the hazards of human spaceflight. One of those topics was on radiation and Dr. Zarana Patel gave us a great perspective on what’s going on and what we’re doing to learn what happens to the body when exposed to space radiation, especially for long periods of time. So, today we’re exploring what’s being done right now to document radiation exposure, not only to make us– to make sure our astronauts are healthy, but to really understand it. So, Dr. Steve Johnson is one of the senior scientists of the space radiation analysis group. Does not only that, but designs hardware, conducts physics modeling and 3D modeling and uses data to plan for future missions. But first I wanted to start with Dr. Patel, who gives us a nice overview of why studying this is so important.
Dr. Zarana Patel:So, to date, there are four health risks from space radiation exposure that we identify. The first one is cancer, the risk of radiation-induced carcinogenesis and that includes epithelial cancers and leukemias, and this is actually the biggest contributor to this permissible exposure limit that– that’s the standard we set for our astronauts. The next one is the risk of in-flight and late CNS decrement. So, CNS is central nervous system, and basically it’s the risk of behavioral or cognitive decrements, either in flight or late post-mission, which can manifest in neurodegenerative disorders like Alzheimer’s.
Host:Oh, wow.
Dr. Zarana Patel:In this one, we’re targeting pathology that can have commonalities between those disorders and cardiovascular disease, which brings me to the next risk, which is the risk of radiation-induced cardiovascular disease. But it’s not just cardiovascular disease, it includes things like cataracts and other degenerative tissue effects, such as immune decrements, respiratory and digestive dysfunction, early aging or premature aging. And, finally, the last one is the risk of acute radiation syndromes. This is really a specific one for solar flares or what we call solar particle events. So, this one is a more intermittent, but large-dose exposure from a solar flare and you have things like skin burns, prodromal responses, nausea. This one is fairly effectively shielded against.
Host:That was a clip from our first episode on the hazards of human space flight, radiation, but today we’re diving deep into our real-time operations dealing with radiation and space weather with Dr. Steve Johnson. So, with no further delay, let’s get right to it. Enjoy.
[ Music ]
Host: Thanks for coming today, Steve. This is an interesting topic. I’m calling it space weather, but it’s– I don’t think it’s exactly what it sounds like. When I think of weather, I think of rains, clouds, I think of thunder, but space weather is a little bit different, isn’t it?
Dr. Steve Johnson:Well, it’s a little different, yes, but it’s similar in that it’s a changing environment. In this case, rather the changing environment of the atmosphere around us. We’re looking at how the environment is changing in space around us. And, in this case, what the parameters that are changing are charged particles, magnetic fields, the solar wind– a lot of different parameters, but in the end it’s the charged particles and the radiation that we’re most concerned about and we want to monitor how that changes with time and what drives us– what drives all of these dynamic changes or changes that occur at the sun on various time scales. And so we want to be kind of solar physicists in a way, but that’s what starts the cold front and warm fronts or whatever, if you will. They have the influences to change how the space environment changes around us.
Host:Really, so it’s mainly an environmental thing. The changing environment, that is the weather, but it seems like the sun is the primary source of that weather.
Dr. Steve Johnson:Yes, it is.
Host:OK. So– and you said– I guess we’ll start with radiation because radiation is probably one of the more significant things that you’re looking at. Right?
Dr. Steve Johnson:Well, that’s our primary purpose is for– we want to monitor the radiation environment for crew health purposes, for radiation health and protection. We also advise the flight team when there are changes in the environment that may be of concern to people that have, say, hardware that are– might have– are sensitive to radiation, but our primary focus is working within– at least for the operations crew within the space radiation analysis group. The operations portion, that’s our primary focus is to watch out for the crew.
Host:Yeah.
Dr. Steve Johnson:And actually it kind of turns around the other way. A lot of times it’s watching out for the flight control team because everybody hears radiation and everybody goes hysterical. You know? And so a lot of times we’re– more often than not, we’re preventing radiation hysteria and saying no, this isn’t a big deal, just calm down and this is– this is fine, you know, we don’t need to do anything. And so, more often than not, that’s our story then the sky is falling.
Host:Yeah, exactly. And it’s not so much, you know, we have to worry about the folks here on Earth, it’s the folks here on Earth worried about what’s going on in space. We’ve got a nice little protective bubble, the magnetic sphere, right, that keeps us kind of safe.
Dr. Steve Johnson:Between the atmosphere and the– Earth’s magnetic field, we get a lot of protection. And the space– and the space station gets a lot of protection from the magnetic field. Most of the time we’re protected. Maybe say 95% of the time we’re protected by the magnetic field and there’s only 5% of the time that we intermittently kind of slip out from underneath this radiation protection umbrella and can see free space radiation and so those are the intervals of times that we’re most concerned with.
Host:Interesting. Yeah, we’ve talked about radiation before on the podcast, mostly from the biological perspective, but not so much from the operational. The day-to-day, you know, here’s what we’re doing every day to make sure the crew is healthy onboard. So, I kind of wanted to start with because radiation is such a big part of space weather, diving into that. What is radiation? Let’s start there.
Dr. Steve Johnson:Well, radiation generally is– in a generic sense, it’s transferring– it’s transfer of energy. In the case– in our case, in our specific application, radiation are– is composed of charged atomic nuclei. Usually they’re fully ionized, so they don’t have any electrons. And they have very high kinetic energies and they will move along at high velocities until they encounter matter of some sort and then they will have interactions primarily with the electrons of the substrate and then they will slowly give up their kinetic energy and when people become that mass that they’re slowing down in, the energy is transferred to the electrons and the electrons are what create all the bonds of all the big molecules, so we’re disrupting those bonds. And when that’s your DNA, if you disrupt those bonds, you’re disrupting the cellular code and you might kill the cell outright or you may have some artifact that’s been modified but still stable enough to be passed on to future generations.
And it’s that type of damage that becomes– the damage of highest concern is that some stable alteration in the DNA code could be carried on.
Host:Wow. So, it’s not really something you feel, kind of, an ever presence thing. It’s something that’s small but high energy and has a lot of impacts over time.
Dr. Steve Johnson:Yeah, that’s right. It’s– you can’t– you can’t feel it.
Host:Yeah. Yeah. So, is a lot of it, you said– like you said, coming from the sun, but is there– is there a part that’s galactic cosmic rays, anything other than the sun too?
Dr. Steve Johnson:Well, the sun gives us the short bursts of radiation that– of high– well, there’s always– there’s always charged particles coming off the sun and that’s called the solar wind and it’s benign. It doesn’t have the sufficient energy to be of concern ever. It’s just the short bursts that we get during solar proton events that protons are accelerated at high enough energies that they can penetrate the spacecraft and penetrate into the person and give them some exposure.
Host:Oh.
Dr. Steve Johnson:Normally, day-to-day, we have two primary sources of radiation. One is the trapped radiation belts or the Van Allen belts, if you will. Those are mostly trapped protons, trapped electrons, and we pass through a certain region of the orbit where that belt comes close to the Earth. And we pass through that about six times a day. And then the rest of the time it’s just kind of this background radiation which is from the galactic cosmic radiation.
Host:Ah.
Dr. Steve Johnson:And the source of that is from outside the– outside the solar system, throughout the galaxy, maybe particles even from galaxies far, far away. And they just have very– you know, created maybe during supernovas and these nuclei are being accelerated at very high energies and much higher than the solar protons or the trapped radiation. They’re very, very penetrating and they’re also– it’s about 90% protons, so you have 10% that’s not protons. And, as the atoms get heavier, they are capable of doing more damage biologically. They’re of more concern and so when we start leaving Earth’s– low Earth orbit to be in free space, whether you’re on the moon or on the way to Mars, the GCR– galactic cosmic radiation– the GCR exposure is increased and becomes more of a threat that, you know, we might exceed what our current limits are.
There’s no reprieve from this chronic low-level radiation that’s very damaging and that becomes a big concern for those types of missions.
Host:You said daily dose of radiation is coming from the ever-present galactic cosmic radiation. It’s still not a lot because of the protection we have because we’re in low Earth orbit versus being out– deeper out into space.
Dr. Steve Johnson:It’s modulated, so it’s– I don’t know, maybe a third or a quarter of what it would be if we were in free space. That’s the total amount of GCR that we receive while we’re in low Earth orbit is about a third or a quarter of what it might be in free space.
Host:Now, I didn’t realize that the– I thought the space station was pretty low, but it seems like it’s peeking out into little bits of the Van Allen radiation belt ever– a couple times a day you said, right?
Dr. Steve Johnson:Well, you can’t– the only way you can avoid the– that region of the trapped radiation belts that comes down real low is known as the South Atlantic anomaly.
Host:Ah.
Dr. Steve Johnson:And very conveniently, it is located over the South Atlantic near South America. It’s slowly drifting west with time, so I guess they may have to rename it after a few decades and– but– because it will be in a different position, but that’s part of the weakening of the magnetic field. The only way to avoid the trapped radiation is to fly at low altitudes and then you’re flying where the atmosphere is thick enough still that it really reduces the amount of radiation from the trapped protons. But if you go to higher altitudes, you get increasingly larger trapped doses.
Host:Yeah, 250 miles above the Earth is a pretty nice spot. It’s high enough where you don’t have to really worry about atmospheric drag too much, just a little bit, you have to reboost every once in a while, but it’s low enough where you’re getting a decent amount of radiation protection.
Dr. Steve Johnson:It works both ways.
Host:Yeah. Yeah, yeah.
Dr. Steve Johnson:OK, less– you know, the atmosphere being like– the atmosphere being an influence on satellite drag, it’s also a drag on protons, on the space radiation, so you have less satellite drag, you have less drag on the protons, so you really start having higher doses. So, there winds up to be this trade that if you want to fly really high and not have reboosts because you’re trying to avoid the drag of the spacecraft– on the spacecraft– you wind up getting more dose. So, there is a– there is a trade there that spacecraft drag wins in the pocketbooks.
Host:Yeah. So, let’s go into what your group does, the space radiation analysis group. It’s got quite a lot of different, I guess, areas that you’re focusing on, but one of them– one of the ones is the– is what we mentioned up front, which is just the day-to-day operations of what’s going on aboard the space station. So, what are you doing to monitor the– what’s the radiation environment of the International Space Station?
Dr. Steve Johnson:We go– we– we’re part of mission control and we go in every day. We report to the flight surgeon and the flight director.
Host:OK.
Dr. Steve Johnson:And we go in every day and fire up our systems and make sure everything is running right, make– check on all our instruments. We have a half dozen radiation instruments that are on the space station. We check on their status, check on the data trends, check on the space weather, what we see. We coordinate with a group in the– with NOAA, National Oceanographic and Atmospheric Administration. They have a group that’s called the Space Weather Prediction Center, which is kind of like the national space weather service, if you will. And we talk to them– and they’re the experts– and we compare notes about what we see for trends and it’s up to us to kind of take what their total outlook is and apply it to our specific situation with our mission. We also– besides checking our instruments, make sure our computer codes are running, up and running.
Check on just the normal admin for being part of mission operations. What’s happen– just what’s happening, you know, on the ground or what the crew schedule is and such things and put that all together. And then we’re on-call. We have two people that are always on-call every day and we’re supposed to be able to respond back within 45 minutes if we get a page and one of our– one of our systems is a server that is ingesting space weather data and if it pulls in values that are above thresholds that we’ve established, then we get email notifications which tells us to come in and NOAA SWPC, space weather predictions center, will also give us a call and let us know. So, we have a little bit of redundancy in terms of how we get notified. We have one server is prime. We have another server that’s doing the same job, but just checking to make sure the first one’s running so it’ll send us a note if it doesn’t– if the prime was not running.
And then the Space Weather Prediction Center has its own email and they follow up with a phone call. So, we’re not likely– and we have two people, so we’re not likely to miss a call in. So, that’s kind of our ops work in a nutshell.
Host:Nice. So, this– I’m trying to think about– you said space weather and you’ll get notified if something is happening. What are some of the events that would be happening that you would get notified and says hey come in in 45 minutes?
Dr. Steve Johnson:Well, the primary thing would be for what we would call an energetic proton event and that would be a situation where an event has occurred on the sun and normally that event is a coronal mass ejection. There’s a couple ways to accelerate protons, but the ones that really generate the events that are the big threat to us are generated by the development of a coronal mass ejection and as that coronal mass is– becomes disconnected magnetically from the photosphere and starts to rise, there’s a shockwave that goes through the corona and accelerates the protons and then that’s what arrives. But, as that develops, there’s a lot of energy that’s being released across the, you know, electromagnetic spectrum. There’s big– there’s large x-ray flares, which becomes our first indication that something goes on– that something’s occurring. You know, why– you know, we get a page if it’s above an M5 flare.
So, we have to go and look and see, well, why did we have that flare? Is that something of importance? Is it of– is it at a location on the sun that’s important or not? And if it is important, we’ll probably also have radio bursts, called type II radio sweeps, radio bursts, type IV, 10-centimeter bursts. I like to refer to them as Dr. Pepper events, 10, two, and four, but if we get those– and that’s usually an indication collectively between a large x-ray flare and the radio burst that there is a proton event occurring and then with our knowledge of– our situational awareness of where the regions are on the sun and what’s the probable threat, we know pretty quick whether we might see protons, you know, quickly or slowly, but we kind of have a feel for being able to anticipate at that point and can respond. And then when we cross those thresholds, SWPC also lets us know.
So, the Space Weather Prediction Center is letting us know the details of the flare, about where it is, how big it was. If they think the protons are going to come up, they have a code that they run that helps try to predict what the probability is just based on the parameters that have been active with the flare as– at the onset of the event.
Host:So, when– I’m guessing you’re getting this data all the time. What do you see normally? Is it kind of going off in all different directions and don’t really have to worry about it coming towards Earth very frequently?
Dr. Steve Johnson:That’s an interesting question. There’s a couple variants of that. One is the sun is usually not very active, so–
Host:Oh, good thing for us, I guess.
Dr. Steve Johnson:Yeah, but it makes it boring for us. You know? Today’s forecast is boring to mostly boring. There’s no sunspots on the sun today. But on the threat end, just when something does occur, it can have a pretty wide longitudinal distribution in terms of influence.
Host:Wow.
Dr. Steve Johnson:Even though– well, we have our best magnetic connection to somewhere on the western hemisphere of the sun. So, if something happens there, we can have protons here almost right away.
Host:Oh.
Dr. Steve Johnson:If it’s on the east side of the sun, we may get protons, but it may take a day or so for them to get above our action levels. I mean we can see them slowly trickle up, but they’re so far away they have to diffuse across the magnetic field lines of the sun and that just takes a while.
Host:Yeah.
Dr. Steve Johnson:So, in some cases we’re directly connected, in some cases we’re not so connected, but the influence can be very wide.
Host:Wow, that’s kind of scary to think that something happening on the west hemisphere if– you would see the effects almost immediately. So, there’s– in that case, I guess, operationally there’s nothing much that you can do? You can’t, you know, shelter in place or anything?
Dr. Steve Johnson:If– when we’re– well, we have a very good example of one that– such an event occurred back in January of 2005 and it’s a good illustration. The protons were arriving before the flare had even finished peaking, so that was unusual just in that fact alone. Plus it was the highest protons that– for a particular energy band that we looked at. Energetic protons were higher than they’ve been in the space program, so we had all this occurring at the same time. Now, the thing was is that the crew happened to be on orbital paths that it was not slipping out from underneath that protection anytime soon, so we had eight hours to– for the orbit to process before we would have the risk of the crew being– encountering extra exposure from the sun. And so they had just gone to bed, so we didn’t do anything.
There wasn’t any shelter for them because there’s no– there wasn’t any influence from the event because of the orbital track.
Host:I see.
Dr. Steve Johnson:And so by the time they got up, the event had decayed a lot and so they just let them do their normal business, which is, you know, working in the lab and such. The lab is pretty well shielded, so it’s a good place to be during an event. It’s a good place to be working so we can continue our ops, you know, we don’t want to stop ops, but, you know, if we need to do that, we, you know, we can make that recommendation. But anyway, we were protected most of the time, so there’s this factor of where you are in your orbit that– that’s our first question when we realize something’s going on is where are we in the orbit and are we approaching one of those regions where we slip out from being not protected and so we start counting down when that’s going to occur because that’s when if we were going to do some sort of shelter sort of thing, if you will, that’s when we would need to take that protection. And that protection would only be for maybe 10 minutes every 45 minutes for a few hours during the day.
Host:Yeah. When you say orbit, do you mean the orbit of the space station around the Earth?
Dr. Steve Johnson:Yes.
Host:So, depending on that position, maybe the– are you thinking the Earth is going to maybe protect the space station and the crew a little bit more?
Dr. Steve Johnson:No. It’s all the magnetic field.
Host:It’s the magnetic field.
Dr. Steve Johnson:The magnetic field of the Earth is not aligned with the spin axis, so it’s tilted.
Host:OK.
Dr. Steve Johnson:And it also doesn’t intersect at the inner– at the center of the planet and so it’s– that offset is– well, that’s part of what– that tilt and offset is what creates the South Atlantic anomaly that we talked about earlier.
Host:I see.
Dr. Steve Johnson:But it also lowers the amount of magnetic protection over the north– northern part of North America over Canada, that’s not very well protected.
Host:OK.
Dr. Steve Johnson:And if you get over the Indian Ocean, west of Australia, that section in the Indian Ocean, when we cross those geographic points, we’re crossing into areas that are not magnetically protected.
Host:I see. So, that’s your first question.
Dr. Steve Johnson:And so that– so that is, you know, are we approaching those regions and if we’re not approaching those regions, then we’re protected. Even if there’s an EVA and we had a big proton event going, if we’re not crossing those specific zones, then there’s no danger, if you will, from the proton event during those–
Host:Yeah.
Dr. Steve Johnson:Until you do that.
Host:So, how much of it is watching out and watching the crew health and how much of it is watching the vehicle health?
Dr. Steve Johnson:Our role is to– is crew health.
Host:Crew health. So, what are you doing–
Dr. Steve Johnson:We just provide notification. We just tell the– we just tell the– I mean the flight director knows anyway. We say, oh, we’re on recall because we had a– we’ve got a proton event going on. So, we go in, once we have an energetic proton event started, we’re on 24-hour coverage. Before, our daily– our normal routine, we only go in for the mornings just to check on everything and then we’re just on-call for the rest of the day and the weekend.
Host:I see.
Dr. Steve Johnson:But once we cross those thresholds for the protons, then we are there 24 hours. But we will remind the flight director, oh, well, we have a proton event, you should notify the other flight control centers so that everybody knows. So, if somebody’s got equipment, you know, just put out that everybody– just put out as a note that everybody can see when those times are and it’s up to them to protect their equipment if they need to do that.
Host:Yeah.
Dr. Steve Johnson:But our purpose is the– strict– is primarily the crew.
Host:Yeah, and providing information to the teams and the crew. Are you watching the crew’s radiation– I guess how much they’re absorbing over time?
Dr. Steve Johnson:Well, we make estimates about what we think they’re going to receive during the course of their mission.
Host:OK.
Dr. Steve Johnson:And then we monitor it daily. We can’t really– we don’t really monitor what their dose is exactly. We monitor what the levels are. So, if the dose rates are higher than we expected, then we know they’re probably getting a little more dose than what we projected at the beginning or vice versa.
Host:OK.
Dr. Steve Johnson:And– so we watch those trends. We watch for those trends to see if there’s a change throughout the mission and once the mission is over we have some idea what the total radiation was just based on the instruments. But more specifically, each crew member has a radiation badge that they wear, a personal dosimeter, and we get that back down when they arrive on the ground.
Host:Oh.
Dr. Steve Johnson:And then that gets analyzed and that gives us the value that will go into their medical records.
Host:OK. OK, so it’s documented, I guess, your total career exposure.
Dr. Steve Johnson:Yes. It’s tracked for all their– each flight there’ll be an entry for what their exposure is. We track it– we track their exposure in terms of percent risk and not necessarily so much dose.
Host:OK.
Dr. Steve Johnson:And so our limits are really based on risk levels.
Host:OK. So, the limits would be– I mean if you’ve flown in space x number of times and been up there x number of days, maybe you have– you’ve absorbed enough radiation where that’s probably your last flight. Is that kind of how it works?
Dr. Steve Johnson:You could get to that point, hypothetically.
Host:OK. Yeah, no, I mean there’s astronauts with hundreds of days, so I know it’s like– it’s not.
Dr. Steve Johnson:It’s a function of– the risk factors vary as you get older.
Host:Oh.
Dr. Steve Johnson:And it varies between the sexes. Women are more radiosensitive than men.
Host:Oh.
Dr. Steve Johnson:And young people are more radiosensitive than old guys like me.
Host:Really? The younger you are, the more sensitive you are to–
Dr. Steve Johnson:Right, because you’ve got your cells are turning over more rapidly and so you’re going through more cell generations. Whereas when– as you get older, cells turn over much more slowly. So, if you have some damage to a cell, there’s– it takes longer to go through those number of generations before you might see that effect, if an effect was to occur. The other part is is that time in your life is that we also– you can also kind of think of it as loss of life, so to speak, quality of life.
Host:Oh, yeah.
Dr. Steve Johnson:If you’re, you know, a 40-year-old astronaut and, you know, there’s some cancer takes 40 years to develop once you’ve had some, you know, event occur, well that makes you 80. Well, people live to be 80, so you’re really kind of still kind of in that zone where that is kind of like a loss of quality of life impact. Whereas if you were 60 years old and flew and takes 40 years for it to develop, you’re 100. Well, are you really having a quality of life issue at that point? Well, no, you’ve kind of– you’re out there where, you know, most people don’t live, so you’re– it’s not really a loss of life effect, so to speak. So, as you get older, there’s less time in front of you for, you know, a cancer to develop or some cardiovascular sort of issue to develop.
Host:I see. So, for a radiation perspective, you’re looking at flying senior citizens. Not so much?
Dr. Steve Johnson:Maybe not.
Host:There’s a lot of other factors besides radiation, isn’t there, for what makes an astronaut successful?
Dr. Steve Johnson:Yeah.
Host:So, I mean you’re watching career exposures. You’re talking about some of the dosimeters and some of the hardware actually measuring these dose rates, both on the astronaut and you said there’s six– you said there’s half a dozen–
Dr. Steve Johnson:I said there’s about a half a dozen.
Host:About a half a dozen.
Dr. Steve Johnson:It kind of changes a little bit.
Host:So, what are the instruments and what are they doing?
Dr. Steve Johnson:Oh my.
Host:Big question.
Dr. Steve Johnson:Yeah, I should have brought a list. Well, let’s start with the simple things.
Host:OK.
Dr. Steve Johnson:The radiation badge sort of dosimeters, they use what’s called TLDs, trans– thermoluminescent dosimeters and they’re little crystals that are radiation sensitive and you zero them out, if you will, fly them, let them get exposed, and you bring them down and then you read them.
Host:Oh.
Dr. Steve Johnson:So, yeah, but– so you don’t find out any information while they’re flying. You only get the data once you get them back down to the ground and analyze them. And we change those out about twice a year.
Host:Oh.
Dr. Steve Johnson:So, every six months we make a measurement. So, it’s– it just kind of gives us an idea of what the average dose is for the six months at different locations. So, you have the same type of measurement over a half– over– I don’t know, a couple dozen locations. We’re reducing that slowly because we’ve characterized the station well enough that we can just kind of go to a few reference points and keep track of the trends. The crew also has a badge that’s similar to that, so that goes up with them and comes down with them and we read that.
Host:OK.
Dr. Steve Johnson:The workhorse that we have is– it’s a– it’s known as a tissue equivalent gas proportional counter. And that’s kind of our workhorse. It gives us– it gives us the amount of– the radiation dose rate. It’s telemeter data, so we’re talking about an active instrument now.
Host:OK.
Dr. Steve Johnson:An active instrument– when I say an active instrument, that means it requires electrical power of some sort.
Host:And you’re getting data more frequently.
Dr. Steve Johnson:And we get data telemetered down every minute from it and so that allows us to check what the exposure rates are during proton events, so we’re watching to see it, you know, how much it goes up when we hit those zones where we’re not really protected in the orbit. It also has a dose rate– a high dose rate alarm for the crew. If for some reason weren’t in communication, they would at least get a– some notification that there is a radiation event going on. So, we had two– we had two of those on– we have two different models on station. We also had some– what are called charged particle telescopes, which are a series of silicon discs, wafers, not very thick, but a stack of them. And so each one is a separate sensor and you line them up and it– and you watch radiation as it goes, penetrates that stack of detectors and look at how much energy is deposited in each of the sensors.
There may be as many as, I don’t know, 10 sensors, and we had a– we’ve had a couple internal instruments that are of that type of design and we have one external instrument that had three units in it that’s located outside. And we’ve also got these newer instruments that– they’re about the size of little– of a oversize USB stick that sticks inside the– the instrument itself sticks into the side of a laptop and it’s also a silicon detector that’s– when I say a silicon detector, I don’t mean it’s detecting silicon, I mean it’s– the material is silicon and you’re watching the radiation as it hits the silicon. And it’s a semiconductor, so it’s basically kind of like a big diode and so you’re watching the signal that comes off, how much energy’s being deposited in that silicon detector as, you know, the– as the day goes on.
And so we have– we’re kind of shifting over to those because they’re much– they’re much more compact sort of instruments than the tissue equivalent proportional counter– TPECs as we acronymize them.
Host:Yeah.
Dr. Steve Johnson:The mass and volume are very important when we start considering going to the moon and to Mars, so having these larger detectors doesn’t make sense from a mass standpoint, so we’re kind of shifting over to using these smaller detectors and having those spread out around the station instead of the little passives. For a variety of reasons.
Host:Yeah. Seems like there’s a lot of instruments, a lot of data, a lot of recording, a lot of monitoring. Is there a database that you’re keeping track of with all of these things?
Dr. Steve Johnson:Yeah, we can go back and– I mean I do it frequently when I’m analyzing old events or whatever. I can always go back and pull up the data from any of the proton events that we’ve had or at any time and look at what the trend was, what the background was for whatever purposes I’m trying to analyze.
Host:Yeah.
Dr. Steve Johnson:And we can do that for all of our instruments.
Host:Is there– is there any sort of predictive models where based on the information you have you can make guesses on what kinds of space weather is going to be happening or is it really just kind of reactive? It just– that’s just the way it is.
Dr. Steve Johnson:In terms of space weather, we’re really in what would be called a nowcast situation. So, we have to watch things evolve. However, we have situational awareness that allows that– we try to develop the skill to now when we have high threats and low threats and most of the time it’s easy to discern that it’s a low threat because these proton events and what leads to them are very, you know, specific sort of situations that aren’t– don’t develop frequently.
Host:Yeah.
Dr. Steve Johnson:So, from that standpoint, we have to, you know, on a day-to-day basis it’s nowcasting. But overall, for the solar cycle, there’s a cycle effect on what the dose rates are to the– to the crews of the station and so as the sun goes through its cycle of being from solar min to solar max, the dose rates are changing as a function of that. And so, based on where we are in the solar cycle, we may adjust what we might project for their dose rate for their mission. And we have some models that try to do that, but it’s not an easy thing to do.
Host:What’s solar min and solar max? What’s happening there?
Dr. Steve Johnson:Part of the sun’s dynamics is it goes through this long-term cycle that we call the solar cycle and it goes from a period of time when there is virtually no sun spots, no features on the sun, and we call that solar minimum.
Host:Minimum activity.
Dr. Steve Johnson:Minimum activity. And the– what’s happening is the sun’s– I was amazed when I– when I learned this. The sun’s magnetic pole is reversing every 11 years.
Host:Whoa.
Dr. Steve Johnson:And so, as it goes through this process of reversing, kind of in the middle of that process when it’s kind of– kind of more toward being neutral, if you will. It’s not really neutral, but kind of in the middle of that, that’s when we start having all the hot– a large number of sun spots and active regions on the sun and the sun is prone to producing these proton events. And then that’s solar maximum. And then the field continues to flip and we get back to a solar minimum. And so, from minimum to minimum, your magnetic polarity reverses. And to get it back to where it was to start with, you really have to go through the cycle twice to get the pole to flip again.
Host:Yeah, that’s right.
Dr. Steve Johnson:And so there’s even and odd cycles. Well– in conjunction with that activity, there is– there is a way– there’s– the output in ultraviolet in a particular wavelength changes between solar min and solar max and that wavelength is ultraviolet and it’s readily absorbed by the atmosphere and it causes the atmosphere to expand. So, when we go to solar minimum, we don’t have as much of that UV radiation coming in and being absorbed by the atmosphere and the atmosphere cools and contracts. And that makes for less spacecraft drag.
Host:Oh.
Dr. Steve Johnson:And so, when– during solar maximum, that ultraviolet output increases, atmosphere expands and becomes drag on the spacecraft. So, that’s why we have this solar min solar max drag on the spacecraft sort of thing. And just as I mentioned earlier, drag on the spacecraft is drag on protons, so when you have less drag on the protons, the dose goes up. The more drag, it goes down. So, during solar minimum– it sounds backwards, but during solar minimum our dose rates may be twice as high as they would be during solar maximum for our day-to-day doses.
Host:Because you have less atmospheric protection because it’s–
Dr. Steve Johnson:Because– yes. Yes.
Host:Wow. That is– that does sound kind of backwards, but then I guess–
Dr. Steve Johnson:And it also– on a larger scale, it’s not due to the ultraviolet, but over– – due to the activity of the sun and the solar wind and such. You also wind up having the same sort of cycle on the galactic cosmic radiation that it also is higher during solar minimum periods than it is during solar maximum periods. So, solar minimum are– we have our highest doses and then solar maximum we have lower doses, but we have the risk of these short bursts from proton events that may add to the crew exposures.
Host:Is it the– is it the increased activity in the sun during solar maximum that’s sort of pushing away the galactic cosmic rays? Is that what– is that kind of what’s happening there? Or is it something else?
Dr. Steve Johnson:Yeah, in a way. It’s the solar wind and a combination of a few things that, you know, the– you know, the particles are coming from very far away and they see– you know, there’s just a little bit of influence and it changes and it just– this far into the solar system, it does make a big difference.
Host:So, this makes me think about deep space missions. If you were planning a deep space mission, from a radiation perspective, what’s the right time? What’s the more appropriate time to send people out to– let’s just say we have gateway around the moon to send people to around the moon. Is it during solar minimum or maximum? Does radiation even play a part in the planning?
Dr. Steve Johnson:It does play a part in the planning because we have to address the issue. Does it determine the timing? Well, if you want to make this a long-term project to be on the moon and go to Mars and not just have one shot sort of things, then you’ve got to just be able to deal with the risk of the exposures. Going during solar minimum times, you’re getting a lot more exposure from the GCR and that’s not– that’s not a good thing, so we have to find ways to kind of try to minimize that dose somehow.
Host:Right.
Dr. Steve Johnson:It’s not easy to shield, but, you know, you go to Mars, you’ve got a big spacecraft, got a lot of mass, so maybe using that mass prudently, maybe you can give yourself more protection. You get a little more protection on the surface of the moon because you’ve got the planetary body giving you, you know, some sort of shielding.
Host:Sure.
Dr. Steve Johnson:But you have to consider it, but I’m not sure you can say one’s a better time than the other. You know?
Host:What about the risk of solar flares or coronal mass ejections? Do you have to– would you want to travel during a minimum just to avoid the off chance that you could be affected during transit?
Dr. Steve Johnson:Well, the thing is is that the solar proton events are easier to shield.
Host:Really?
Dr. Steve Johnson:Because they’re lower energy. So, you can make a shelter, if you will, that can make a significant impact on the short-term events. So, in some ways, you know, the better time to go might be during– if you’re just trying to pick one time, you know, solar maximum may be a kind of a better time because–
Host:Lower overall dose, maybe?
Dr. Steve Johnson:That– the low– the background radiation levels are at their lowest, which is what you really care about, and then the short-term bursts that are maybe high dose rate, you can shield against them. Plus their– the damaging capability of the protons is not the same as the higher atomic number of species that you have in the GCR.
Host:So, are you looking at mostly low Earth orbit when you’re looking at all this data for radiation and monitoring the crew health, or are you really looking further out into space, you know, beyond the Earth, maybe towards the moon, Mars, in-between, to understand the environment for deep space missions?
Dr. Steve Johnson:Well, I think we get a feel for what the environment is in general. I mean specifically we’re flying low Earth orbit, so our application is for low Earth orbit, but it’s also– we know what’s happening here locally and the moon’s not that far away, really, so what we see here is– would– is also same thing for the moon. So, whatever our practices are in terms of monitoring– kind of in the cislunar neighborhood, we’re good.
Host:That’s good. Yeah, you don’t have to rewrite everything. Yeah. That’s good. What– and now for Mars, I’m assuming it’s just going to be a little bit different. Maybe communication is an issue because if a solar activity happens, you have to deal with the communication delay.
Dr. Steve Johnson:That– we’re not– we’re still kind of working through how we might want to deal with such things. We also need more longitudinal monitoring of the sun from other angles because what we see here on Earth may not be what’s being influencing a spacecraft on it’s way to Mars or at Mars. So, it may– you know, more resources are going to be needed in order to be able to do some– to do– just to monitor the space weather so we can do our forecasting and analysis and keep the crew advised.
Host:So, are you talking about like satellites and probes to go out kind of towards different areas and fill in those gaps? OK.
Dr. Steve Johnson:Be able to see the sun from different angles.
Host:Yeah.
Dr. Steve Johnson:We had that opportunity over the last decade or so that we’ve had what was called the stereo mission, which sent a pair a of space weather monitoring spacecraft, one ahead in orbit and one kind of lagging the Earth orbit and going around the sun very slowly. It took a decade or so to get to the far side of the sun and then they switched and now they’re kind of coming back. But, that other perspective of the sun– we need to be able to see from those other angles to really– to do the right job to support a Mars mission.
Host:So, thinking about that– and we can sort of wrap up with this idea– what sorts of other gaps do we need to fill to make a deep space mission, like a one to Mars, successful? Especially from a radiation perspective.
Dr. Steve Johnson:Well, I think the physics– we kind of know the physics. So, we know– we have the type of technical information to work on shields and maybe try to optimize some shield designs to try to provide a little bit of more protection. The big question– and I think we can respond to the short-term influences of proton events and such, but the big question is going to be the effects of the chronic exposure to the galactic cosmic radiation. The radiobiology, I think there’s just a lot that we still don’t know. That doesn’t mean we– I don’t know that that stops us from going, but– I don’t know that we’ll ever have all the answers, but I think trying to get a handle on some of that is a very big challenge.
Exposures to– I mean we understand that– well, I say we understand– I mean– radiation and cancer, that’s kind of understood in a way. I mean it’s a stochastic process in that it’s random whether you get an exposure and whether cancer develops, but some other things– some other effects– there’s not really a good way to quantify them and– for example, the neurological effects, getting radiation damage to your neural systems, what, you know, neurons don’t grow back very quickly. You know? So, if you wind up killing off neurons here and there, that’s not good. And there may be other effects that are– maybe with time that, you know, we’ll know more about, but I think they’re still hard to quantify, some of them, and those will always be a– those will always be a challenge I think that’s going to be hanging out there to understand.
Host:That seems to be a theme is there is so much that we don’t know and that’s the– I guess the beauty of science is the more you learn, the more you realize that there’s more to learn. And– but that should never stop you from exploring and I think that’s what’s awesome about NASA is you just kind of keep going. You keep pursuing and it’s this drive to explore that keeps us going out further. I love it. So, thank you, Steve, for coming on and talking about space weather and radiation, opening our eyes to this– I guess not-seen part of spaceflight that’s essential to understand to make it successful, so I appreciate you coming on.
Dr. Steve Johnson:Yeah. Well, it is kind of an unseen thing. We sit in the back room and nobody sees us as we come and go. I could go throw in a story for that real quick.
Host:Yeah, do it.
Dr. Steve Johnson:Just to finish on a– maybe a fun note. I was– I don’t know, I think it was the fourth of July and I was in on the holiday. We– because at the time we went in every single day and– like I said, we sit in a back room, so we’re never really seen. And gone down to the Coke machine and get something to drink and the flight director comes out of the bathroom and she walks up and she sees me standing there and looks and are you– are you one of the radiation guys? And I go oh, yes, yes, yes, she knows who I am. Yes. Yes, I’m one of the radiation guys. She goes is it a bad thing that you’re here? No, no, we’re just here for our regular shift. She was concerned that there was some proton event going on and it wasn’t going to be a quiet day. So, OK, no. It’s a nice day on the sun.
Host:All right. Well, I guess maybe soon it will be a good day whenever people see you come out of the back room a little bit. All right. Thank you, Steve.
Dr. Steve Johnson:OK. Thank you.
[ Music ]
Host:Hey, thanks for sticking around. So, today we talked with Dr. Steve Johnson. We talked about space weather, radiation, and really understanding the sun and how that affects our day-to-day operations for human space flight. We talked earlier about the hazards of human space flight. We have a couple episodes on those, five to be exact, plus a little intro. So, you can go back and watch– or listen– to those episodes. The five hazards of human space flight, nasa.gov/johnson/HWHAP, that is our site. Or wherever you’re subscribed to Houston, We Have a Podcast. We also work with the human research program to come up with some supplementary materials for those. So, if you go to nasa.gov/HRP, they have a section there called the five hazards of human spaceflight and you can click on the radiation section, space radiation, and they have a lot of extra materials if you want to really learn more about the radiation environment. Otherwise, you can go to nasa.gov/iss or one of our many social media accounts for the International Space Station on Facebook, Twitter, and Instagram to know what’s going on 250 miles above our heads. Use the #AskNASA on your favorite platform to submit an idea for the show.
So, this podcast episode was recorded on August 14, 2018. Thanks to Alex Perryman, Bill Stafford, Bill Foster, Pat Ryan, and Isidro Reyna. Thanks again to Dr. Steve Johnson for coming on the show. We’ll be back next week.